This invention relates generally to radio frequency antennas and more particularly to array antennas adapted to operate with circularly polarized radio frequency energy.
As is known in the art, it is frequently desired to provide an array antenna adapted to operate with circularly polarized radio frequency energy over relatively large scan angles. In one such array antenna a plurality of antenna elements are disposed along a linear path, each one of the antenna elements includes a double-ridged flared radiating structure fed to establish linearly polarized radio frequency energy; i.e. radio frequency energy having its electric field vector disposed normal to the wide surfaces of the antenna element. An externally mounted polarizing structure is then disposed between free space and the array antenna elements to convert the linearly polarized radio frequency energy provided by the antenna elements to circularly polarized radio frequency energy on transmit and to convert, on received, circularly polarized energy in free space to linearly polarized radio frequency energy for collection by the array antenna elements. In the array antenna described above, the polarizing structure is wrapped around the front and side portions of the arrayed antenna elements. While such antenna provides satisfactory results when operating over relatively small scan angles, as the beam provided by the antenna is scan to relatively wide scan angles, .+-.60 degrees from boresight, for example, the gain of the antenna at such large scan angles decreases significantly thereby reducing the effectiveness of the antenna at such large scan angles.